The present invention relates to controlling work in process flows through a production environment, and more specifically, to a method that determines whether there is available tool capacity to process a non-committed lot through each required time sensitive processing sequence before releasing that lot to the processing sequence.
One aspect of managing production environments relates to controlling the release of work in process (WIP) into process time windows for factories with a diverse product mix and shared resources. A process time window (PTW) is a manufacturing process requirement where two or more operations must be completed within a period of specified length. Process time window violations can cause product rework or scrap. Shared resources are manufacturing equipment (tools) that are used to process multiple product types.
An issue associated with work in process that is subject to process time window constraints is that tools within process windows are often shared by many product flows, some with time constraints, some without. Further, some tools are not reliably available, and all tools have variability in availability. In addition, the production priority scheme for the products produced by the production environment must be maintained. Some product flows are very long and complex (e.g., over 500 process steps and over 4 weeks of processing time) and some fabrication product flows have from a handful up to 30 process time windows. Also, the trend is for newer product flows have more process time windows.
Therefore, controlled release of WIP is necessary to properly manage process time windows. In some manufacturing environments, production tools must process a mix of time constrained and non-time constrained WIP. This presents two problems for those dispatching WIP to such tools. First, it is difficult to identify time sensitive/non-time sensitive WIP in the queue for the machine/equipment starting the process time window. Secondly, while there are methods for deciding how much time sensitive WIP can be processed, it is still difficult to know how to prioritize and dispatch a mix of time sensitive and non-time sensitive WIP for optimal tool utilization and to meet supply chain objectives.